Hoping it's new bosses, this game has the perfect reason as to why it's new bosses, and the Koopalings, sure they could go for another round but personally I feel like they've overstayed their introduction. Give it a break for a little.
I'm talking as in, every game's OST is bunched up together and you can only pick one from it. What's your most favourite?
If I had to choose, it'd be Dire Dire Docks.